A two-component signal-transducing system is involved in competence and penicillin susceptibility in laboratory mutants of Streptococcus pneumoniae

Penicillin resistance in Streptococcus pneumoniae has been attributed so far to the production of penicillin-binding protein (PBP) variants with decreased affinities for β-lactam antibiotics. Cefotaxime-resistant laboratory mutants, selected after several steps on increasing concentrations of this β-lactam, become deficient in transformation as well. A DNA fragment conferring both cefotaxime resistance and transformation deficiency was isolated and cloned from the mutant C306. The cefotaxime resistance associated with this resistance determinant was not accompanied with apparent changes in PBP properties, and it mapped on the chromosome distinct from the known resistance determinants, genes encoding PBP2x, PBP1a or PBP2b. Determination of a 2265 bp DNA sequence of the resistance determinant revealed two open reading frames, claR and claH, whose deduced amino acid sequence identified the corresponding proteins as the response regulator and histidine kinase receptor, respectively (members of the two families of bacterial signal-transducing proteins). Two hydrophobic peptide regions divided the histidine kinase ClaH into two putative domains: an N-terminal extracelluiar sensor part, and an intracelluiar C-terminal domain with the conserved His-226 residue, the presumed phosphorylation site. The single point mutations responsible for cefotaxime-resistance and transformation deficiency of C306 and of another two independently isolated cefotaxime-resistant mutants were each located in the C-terminal half of ClaH. A small extracellular protein, the competence factor, is required for induction of competence. Neither C306 nor the transformants obtained with the mutated claH gene produced competence factor, and exogenous competence factor could not complement the transformation deficiency, indicating that the signal-transducing system cia is involved in early steps of competence regulation.     

Age-related nonrandom chromosomal abnormalities in human low-grade astrocytomas

We report a cytogenetic investigation of 55 low-grade astrocytomas in 52 patients, 15 children and 37 adults. In addition to numerical aberrations such as trisomy 7 and gonosomal losses, we found structural and/or numerical aberrations of chromosome 1 in eight astrocytomas. There was a striking difference between the rearranged chromosomes in pediatric and adult patients. Whereas the pediatric tumors revealed monosomies 1p with accompanying trisomy 1q, the astrocytomas in adults showed partial or complete monosomies 1q.     

Back to log phase: σS as a global regulator in the osmotic control of gene expression in Escherichia coli

It is now well established that the σ^S subunit of RNA polymerase is a master regulator in a complex regulatory network that governs the expression of many stationary-phase-inducible genes in Escherichiacoli. In this review, more recent findings will be summarized that demonstrate that σ^S also acts as a global regulator for the osmotic control of gene expression, and actually does so in exponentially growing cells. Thus, many σ^S-dependent genes are induced during entry into stationary phase as well as in response to osmotic upshift. K⁺ glutamate, which accumulates in hyperosmotically stressed cells, seems to specifically stimulate the activity of σ^S-containing RNA polymerase at σ^S-dependent promoters. Moreover, osmotic upshift results in an elevated cellular σ^S level similar to that observed in stationary-phase cells. This increase is the result of a stimulation of rpoS translation as well as an inhibition of the turnover of σ^S, which in exponentially growing non-stressed cells is a highly unstable protein. Whereas the RNA-binding protein HF-I, previously known as a host factor for the replication of phage Qβ RNA, is essential for rpoS translation, the recently discovered response regulator RssB, and ClpXP protease, have been shown to be required for σ^S degradation. The finding that the histone-like protein H-NS is also involved in the control of rpoS translation and σ^S turnover, sheds new light on the function of this protein in osmoregulation. Finally, preliminary evidence suggests that additional stresses, such as heat shock and acid shock, also result in increased cellular σ^S levels in exponentially growing cells. Taken together, σ^S function is clearly not confined to stationary phase. Rather, σ^S may be regarded as a sigma factor associated with general stress conditions.     

Continuous Synthesis of (R)-(+)-Benzaldehydecyanohydrin Using (R)-Oxynitrilase in Lyotropic Liquid Crystals

The possibility of using the enzyme (R)-Oxynitrilase in a biphasic lyotropic liquid crystal/dibutylether system has been demonstrated. This reaction system is applicable for the continuous production of (R)-benzaldehydecyanohydrin in a fixed bed reactor. The optical purity was between 94 and 96% ee and independent of the flow rate. The space time yield was maximal (2650 g/(1*d)) at a flow rate of 1.6 ml/min.     

Enhancement of specific nitrogenase activity inAzospirillum brasilense andKlebsiella pneumoniae,inhibition inRhizobium japonicum under air by phenol

Specific nitrogenase activity inAzospirillum brasilense ATCC 29145 in surface cultures under air is enhanced from about 50 nmol C₂H₄·mg protein^-1·h^-1 to 400 nmol C₂H₄ by the addition of 1 mM phenol. 0.5 and 2 mM phenol added increase the rate 5-fold and 4-fold. This enhancement effect is observed only between 2 and 3 days after inoculation, with only a small reduction of the growth of the cells by the phenol added. In surface cultures under 1% O₂, nitrogenase activity is slightly reduced by the addition of 1–0.01 mM phenol. Utilization of succinate is enhanced during the period of maximum enhancement of nitrogenase activity by 60% by addition of 1 mM phenol. The cells did not produce¹⁴CO₂ from [U-¹⁴C] phenol, neither in surface cultures nor in liquid cultures and less than 0.1% of the phenol was incorporated into the cells. A smaller but significant enhancement of nitrogenase activity by about 100% in surface cultures under air was found withKlebsiella pneumoniae K 11 after addition of 1 mM phenol. However, inRhizobium japonicum 61-A-101 all phenol concentrations above 0.01 mM reduced nitrogenase activity. With 1 mM phenol added activity was reduced to less than 10% with no effect on the growth in the same cultivation system. With thisRhizobium japonicum strain significant quantities of phenol (25 mol in 24 h by 2·10¹² cells) were metabolized to¹⁴CO₂, with phenol as sole carbon source. WithAzospirillum brasilense in liquid culture under 1% and 2% O₂ in the gas phase, no enhancement of nitrogenase activity by phenol was noticed.     

Evaluation of synthetic sex pheromone for monitoring and management of raspberry crown borer Pennisetia marginata (Lepidoptera: Sesiidae)

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The Crossmodal Congruency Task as a Means to Obtain an Objective Behavioral Measure in the Rubber Hand Illusion Paradigm

The rubber hand illusion (RHI) is a popular experimental paradigm. Participants view touch on an artificial rubber hand while the participants'' own hidden hand is touched. If the viewed and felt touches are given at the same time then this is sufficient to induce the compelling experience that the rubber hand is one''s own hand. The RHI can be used to investigate exactly how the brain constructs distinct body representations for one''s own body. Such representations are crucial for successful interactions with the external world. To obtain a subjective measure of the RHI, researchers typically ask participants to rate statements such as "I felt as if the rubber hand were my hand". Here we demonstrate how the crossmodal congruency task can be used to obtain an objective behavioral measure within this paradigm.The variant of the crossmodal congruency task we employ involves the presentation of tactile targets and visual distractors. Targets and distractors are spatially congruent (i.e. same finger) on some trials and incongruent (i.e. different finger) on others. The difference in performance between incongruent and congruent trials - the crossmodal congruency effect (CCE) - indexes multisensory interactions. Importantly, the CCE is modulated both by viewing a hand as well as the synchrony of viewed and felt touch which are both crucial factors for the RHI.The use of the crossmodal congruency task within the RHI paradigm has several advantages. It is a simple behavioral measure which can be repeated many times and which can be obtained during the illusion while participants view the artificial hand. Furthermore, this measure is not susceptible to observer and experimenter biases. The combination of the RHI paradigm with the crossmodal congruency task allows in particular for the investigation of multisensory processes which are critical for modulations of body representations as in the RHI.